Film tensioning apparatus



Oct. 9, 1951 C. C. DAVIS FILM TENSIONING APPARATUS Filed Dec. 6, 1949 /Nl/EA/ TOR C. C. 0,4 I//S BV n vf/f 7% ATTORNEY Patented ct. 9, 1951 FILM TENSIONING APPARATUS Charles C.l Davis, West Los Angeles, Calif., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application December 6, 1949, Serial No. 131,342

3 Claims. (Cl. 271-23) This invention relates to mechanical illters used in lm propelling mechanisms employed in sound film recording and reproducing apparatus and particularly to improvements in such filters of the double roller type in which the pivoted supporting arms for the film engaging rollers are interconnected by a single spring.

Heretofore, mechanical lters of the double drives in which the nlm path is the same with respect to each roller so that the film tension produces in each roller an equal resultant force at right angles to the length of the roller supporting arms. Therefore, to equalize the tension in the film on both sides of a lm supporting drum, it is necessary only to produce an equal opposing force in each roller, which can be done readily by a single interconnecting spring having its ends permanently anchored in the roller supporting arms at predetermined points along these arms.

This relatively inexpensive type mechanical filter has proven so successful in eliminating disturbances in the film at the sound translation point that its use is contemplated as an attachment -for existing equipment, such as, a motion picture camera modified to include a sound recording equipment. The greatest diiliculty encountered in such modification is the impossibility in most cases of obtaining space within the camera housing in which the film path is the same with respect to both iilm engaging rollers of the mechanical filter. Also, for one type of camera,

the film path with respect to each roller will be different from the iilm path encountered in another type of camera, so that, a filter mechanism as provided heretofore and designed for one camera, cannot be used with success in another type camera wherein the fllm path is different. A' dii'- ference in the film path withfrespect to the two rollers of the filter will produce a difference in the force exerted on the rollers by the nlm tension, thus requiring an opposing force in one rollerfwhich is greater than the opposing force in the other roller.

In existing' equipment of this type, the space available for locating the sound recording unit is usually quite limited. With limited space. the roller and supporting arm elements of the filter and the nlm supporting drum must. he reduced in size. In using smaller elements there is introduced the possibility of a greater variation in friction inthe bearing of the separate sets of rollers and scanner drums. A difference in friction in the bearings in the separate set of similarly designed filter units will produce a condition wherein to obtain equalization of the lm tension on both sides of the nlm supporting drum, it will be necessary to produce different opposing forces in the two rollers to compensate for the change in nlm tension introduced by the change in friction in the bearings.

It is the object of this invention to provide a mechanical filter of the double roller vtype incorporating meanspermitting independent adjustinent of the force exerted by each roller on the film whereby the mechanical filter may be adapted for efllcient operation in all lm drives regardless of the film path with respect to the separate rollers.

A -feature of the vinvention resides in the provision of a double roller mechanical filter incorporating an interconnecting spring between the parallel roller supporting arms, the spring being so disposed with respect to these arms and anchored thereto in such manner that the length of the acting radius of the spring with respect to each arm may be independently adjusted to vary the force exerted by each roller on the lm.

The invention will be more readily understood by reference to the following specification when read in connection with the accompanying drawing in which:

Fig. 1 is a view in elevation of a camera film drive in which a mechanical filter and film supporting drum have been added in accordance with this invention; and

Fig. 2 is a diagram of the forces acting on the upper lter roller in the drive as shown in Fig. 1.

Referring to Fig. l, a film F is driven in the direction indicated by the arrow by a toothed driving sprocket I. A sprocket 2 engages the lm F and feeds it to a suitable take-up reel (not shown). |I'he loop of film between sprockets 1 and 2 engages and produces rotation of a freely rotatable drum 3, whichl supports the film F at the sound recording point. Drum 3 is rotatable on a suitable bearing on a stud 4 secured to the camera housing. Prior to engagement of film F with drum 3, it is engaged by a roller 5, which is freely rotatable in the end of a supporting arm 5. The other end of arm 6 is pivoted on the camera housing at l. The film leaving roller 3 is engaged by a roller 8, which is freely rotatable in the end of a supporting arm 9. Arm 9 is pivoted on the camera housing at I0.

The two arms 6 and 9. are interconnected by a spring Il in a manner to urge the rollers 5 and 8 against the film on opposite sides of drum 3. A threaded stud I2 engages an internally threaded roller 5. One end of spring II' is anchored to theend of stud I2 extending above arm 8. A

circular aperture 2l.. If, with the illm threaded in the machine, the line I9 appears at the center of aperture 2l, the arms 6 and 9 are parallel and threaded stud I3 engages an internally threaded i hole in arm 9 between the pivot point I9 and the roller 8. The other end of spring II is anchored to the endvof stud I3 below the arm 9.

Stud I2 may be rotated in a manner to increase or decrease the length thereof extending above arm 6 to thus increase or `decrease the length of the acting radius R of spring II on arm 6. Similarly, stud I3 may be rotated in a manner to lncrease or decrease the length thereof extending below arm 9 to thus increase or decrease the length of the acting radius R' of spring II on arm 9. -An increase in the acting radius R will increaselthe downward force exerted by spring li on arm 6 which, in turn, produces an increase in the force exerted by roller 5 on the nlm F. Similarly, an increase in the acting radius R will increase the downward force exerted by spring ii on arm 9 which, in turn, produces an increase in the force exerted by roller on the iilm F.

lt will be seen that by means of the novel arrangementof the spring interconnecting the two roller supporting arms 5 and 9, the force exerted by each roller on the iilm may be independently adjusted to compensate individually for the difference in the lm tension force acting against the rollers due to a difference in the illm path with respect to each roller.

A typical example of a nlm path likely to be encountered in a camera lrn drive is shown in Fig. l. As shown, the film F approaches the roller 8 from drum 3 at an angle of 25 degrees to the horizontal. The nlm after passing under roller leaves the surface thereof at an angle of 48 degrees to the horizontal to contact with sprocket 2. Assuming a lm tension of 300 grams at a point A, a reference to the diagram of forces inY Fig. 2 will show that for a nlm tension of 300 grams a vertical force of 350 grams is exerted by the lm on roller 8. It will, therefore, be necessary to produce an opposing force in roller d equal to the 350 grams, whereas in roller 5, because ofthe vertical path of the film from this roller to sprocket i, it will be necessary to produce an opposing force of only 300 grams, which is the iilm tension at point B.

As stated above, separate sets of similarly manufactured mechanical filters and scanner drums may vary as to bearing friction. An increase in bearing friction in the rollers over an allowable maximum is likely to produce an appreciable increase in the normal 300-gram fllm tension at the point A, thus requiring a further adjustment by means of stud I3 to produce an additional increase in the opposing force exerted by roller 8 on the fllm to equalize the tensions produced in the lm on opposite sides of the drum 3. If the hlm F in the drive shown was driven in a direction opposite to that shown by the arrow, an increase in the normal 300-gram lm tension caused by bearing friction would appear at point B, thus requiring an increase in the downward force exerted by roller 5 on the nlm.

Means for damping resonant oscillation of the mechanical lter is provided in the form of an oil dash pot comprising a stationary oil-lled chamber I5 and a movable plunger I6 pivoted to arm 6 at I'I.

A hn threading target isfprovided in the form of an element I8 attached to arm 9 and provided with a line mark I9. A second element of the therefore meet one requirement for correct operation of the filter mechanism. The arms 6 and 9 in the mechanical lter shown in Fig. 1 must not only be parallel but they must also be horizontal to be in correct operating position with respect to drum 9.

.When the film driving mechanism is in operation, the stud I2 may be adjusted in arm 8 by rotating a knurled element 25 attached to the end of this stud. A similar knurled element (not shown) may be provided on the end of stud I 9. These studs may be adjusted during operation of the film drive until the target position is obtained for correct operating position of the arms E and 9. It is possible that after final adjustment of the mechanical filter, the arms 5 and 9 will be parallel as indicated by the target but that these arms will not be quite horizontal. It has been found that a slight Vernier adjustment of one of the studs will correct this condition without adversely affecting the force adjustment of the rollers.

that the mechanical filter provided in accordance with this invention may be incorporated into any existing film drive and readily adjusted to produce tension equalization in the film on opposite sides of the drum supporting the lnlm at the recording or reproducing point.

What is claimed is:

l. The combination in a sound illm recording or reproducing apparatus provided with a rotatable drum supporting said lm at an exposure point, of a mechanical filtering means, said ltering means comprising a pair of pivoted arms, each of said arms having a film engaging roller mounted in the free end thereof, the two said rollers engaging said lm on opposite sides of said drum, a spring disposed substantially parallel to and interconnecting said pivoted arms to produce movement thereof in a direction to cause said rollers to engage said film, and means anchoring the ends of said spring to said arms, each said anchoring means being individually adjustable toward and away from its associated arm to vary the acting radius of said spring separately with respect to said arms.

2. The combination in a light film recording or reproducing apparatus provided with a light exposure point and a rotatable drum supporting said f'llm at said exposure point, of a mechanical ltering means comprising a pair of pivoted arms each having a film engaging roller mounted in the free end thereof, the two said rollers engaging said i'llm on opposite sides of said drum, a spring disposed substantially parallel to said arms, a stud extending from each of said arms with the free end thereof engaging an end of said spring, each of said studs being adjustable in its associated arm to vary the acting radius of said spring separately with respect to said arms to permit equalization of the force exerted by said rollers on saidlm on opposite sides of said drum.

3. The combination in a sound lm recording and reproducing apparatus provided with a light exposure point and a rotatable drum supporting said film at said exposure point, of a mechanical ltering means comprising a pair of parallel pivoted arms each having a film engaging roller mounted -in the free end thereof, said lm entarget is attached to arm I5 and provided with a 75 gaging each of said rollers on the underside It will be apparent from the above description `5 f B thereof, a 'spring disposed substantially parallel REFERENCES CITED to and between said arms, one end of said spring being anchored to one of said arms between its pivot and its roller carrying end, the other end The following references are of record in the iile of this patent:

of said spring being anchored to the other of 5 UNITED STATES PATENTS said arms at the end thereof opposite its pivot Number Name Date from its roller carrying end, and means permit- 1,831,562 Heisler Nov. 10, 1931 ting adjustment of each anchorage toward or 2,442,400 Collins June 1,1948 away from its associated arm to vary the acting radius of said spring with respect to each arm. 10 FOREIGN PATENTS Number Country Date CHARLES C. DAVIS. 370.001 Great Britain Mar. 24, 1932 

